In recent years, the substantial increases in costs of basic materials such as metals, metal alloys, plastics, rubbers and the like has encouraged development and use of light weight structural materials, strength adding materials and of filler materials to reduce the amount and cost of the basic materials used and the weight of the finished materials.
The known methods for producing hollow metal microspheres have not been successful in producing microspheres of relatively uniform size or uniform thin walls which makes it very difficult to produce materials of controlled and preditable characteristics, quality and strength.
One of the existing methods of producing hollow metal spheres is disclosed in the Hendricks U.S. Pat. No. 4,133,854. The method disclosed involves dispersing a blowing gas precursor material in the metal to be blown to form the microspheres. The material containing the blowing gas precursor enclosed therein is then heated to convert the precursor material to a gas and is further heated to expand the gas and produce the hollow microsphere containing therein the expanded gas. Another process for making hollow metal spheres is disclosed in Niimi et al, U.S. Pat. No. 4,021,167. This method involves dropping molten metal stream through a nozzel, passing the molten jet metal through a linear water jet which fragments the molten metal into droplets and traps water droplets in the droplets of molten metal. The trapped water droplets expand inside the molten metal droplets to thereby form hollow metal particles.
These processes, particularly the Niimi et al process, are understandably difficult to control and of necessity, i.e. inherently, produce spheres varying in size and wall thickness, spheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial number or proportion of microspheres which are not suitable for use and must be scrapped or recycled.
In addition, the filamented microspheres of the present invention provide a convenient and safe method of handling the microspheres.
The known methods for producing hollow metal microspheres have not been successful in producing microspheres of uniform size or uniform thin walls and in producing hollow metal microspheres of controlled and predictable physical and chemical characteristics, quality and strength.